1. Field of the Invention
The invention relates to an organic thin film transistor structure and a fabrication method thereof. Particularly, the invention relates to a bottom contact organic thin film transistor structure and a fabrication method thereof.
2. Description of Related Art
In a conventional technique domain, organic thin film transistors are divided into two types according to structures thereof, which are top contact organic thin film transistors and bottom contact organic thin film transistors.
Referring to FIG. 1, FIG. 1A is a cross-sectional view of a conventional top contact organic thin film transistor 110. When the top contact organic thin film transistor 110 is fabricated, deposition of an organic layer serving as an active layer 113 is first performed, and then deposition of a source 111 and a drain 112 is performed. Generally, an organic semiconductor material of the active layer 113 is sensitive to moisture and oxygen in atmosphere and solvent. Moreover, a chemical solvent (for example, a developer) used in a photolithography process may cause certain damage to the organic material, so that the photolithography process cannot be used to pattern the deposited source 111 and drain 112. Instead, a metal mask is used to achieve a partial deposition effect. However, a device size of the organic thin film transistor 110 fabricated according to the above method is limited to a gap size of the metal mask, which is of no avail for integration and mass production of the organic thin film transistors.
Referring to FIG. 1B, FIG. 1B is a cross-sectional view of a conventional bottom contact organic thin film transistor 120. When the bottom contact organic thin film transistor 120 is fabricated, deposition of an active layer 121 is performed last, so that a source 122 and a drain 123 can be fabricated through a general photolithography process. Compared to the aforementioned top contact organic thin film transistor 110, the bottom contact organic thin film transistor 120 is adapted to be used in small size devices. However, in the bottom contact organic thin film transistor 120, flatness of a contact surface between the active layer 121 and the source 122 and the drain 123 serving as electrodes is poor, so that an electrical characteristic of the bottom contact organic thin film transistor 120 is inferior to that of the top contact organic thin film transistor.